Pickup trucks generally comprise a frame assembly having a front end supporting a cab for carrying passengers and a rear end supporting a cargo box, also called bed, for carrying cargo.
A cargo box for a pickup truck typically includes a base panel bounded by upstanding walls to form a container. The walls include two side walls, a front wall and a rear wall. The rear wall may be pivotably mounted to provide a tailgate facilitating the insertion or removal of articles in the cargo box. Each side wall includes a wheel casing which protrudes into the cargo box and which is destined to be placed above a rear wheel of the vehicle.
The walls of the cargo box are each generally made of an inner panel being a structural part and an outer panel being an ornament panel.    The inner panels are each generally made of a metallic material, for example steel. For example, it is known to produce the cargo box by providing a steel blank for each inner panel and by stamping the blanks so as to shape the panels. In particular, each side panel is produced from a one-piece blank, i.e. a blank obtained by cutting a single steel sheet.